Pyrolytic carbon coatings have been used to protect particles of nuclear reactor fuel, i.e., fissile and/or fertile materials, such as uranium, plutonium and thorium in the form of suitable compounds thereof. Coatings of aluminum oxide and other ceramic oxides have also been proposed. Examples of nuclear fuel particles employing pyrolytic carbon coatings include U.S. Pat. No. 3,325,363, issued June 13, 1967; No. 3,298,921, issued Jan. 17, 1968, and No. 3,361,638, issued Jan. 2, 1968. It is also known to incorporate one or more layers of refractory carbide materials, such as silicon carbide or zirconium carbide, to produce nuclear fuel particles having still better fission product retention characteristics, as disclosed in U.S. Pat. No. 3,649,472, issued Mar. 14, 1972. So long as these fission product retentive coatings remain intact, contamination exterior of the particles by the heavy metal fuel material and/or substantial spread of fission products exterior of the coatings is prevented.
Nuclear fuel particles of this type are generally bonded together in some fashion to create an object which is termed in the art either a nuclear fuel compact or, depending upon its size, nuclear fuel element. It has been found that fracture and/or cracking of the fission-product-retentive-coatings can occur during the formation of these larger objects wherein the nuclear fuel particles are combined with a matrix material of some type. As a result, the search continues for improved nuclear fuel particles which are better suited for manufacturing processes of this type wherein they will be combined into larger objects with the use of such a matrix material.